This application relates generally to receiver circuits and, in particular to a CATV tuner with a frequency plan and architecture that allows the entire receiver, including the filters, to be integrated onto a single integrated circuit.
Radio receivers, or tuners, are widely used in applications requiring the reception of electromagnetic energy. Applications can include broadcast receivers such as radio and television, set top boxes for cable television, receivers in local area networks, test and measurement equipment, radar receivers, air traffic control receivers, and microwave communication links among others. Transmission of the electromagnetic energy may be over a transmission line or by electromagnetic radio waves.
The design of a receiver is one of the most complex design tasks in electrical engineering. In the current state of the art, there are many design criteria that must be considered to produce a working radio receiver. Tradeoffs in the design""s performance are often utilized to achieve a given objective. There are a multitude of performance characteristics that must be considered in designing the receiver. However, certain performance characteristics are common to all receivers. Distortion and noise are two such parameters. The process of capturing the signal creates distortion that must be accounted for in the design of the radio receiver. Once a radio signal is captured, the noise surrounding the received signal in the receiver must be considered. Radio signals are often extremely weak and if noise is present in the circuit, the signal, even though satisfactorily received, can be easily lost in this noise floor. The current state of the art in receiver design is often directed to overcoming these receiver limitations in a cost effective manner.
There is therefore provided in a present embodiment of the invention, a fully integrated tuner architecture having all channel selectivity and image rejection integrated onto a single silicon substrate.
An embodiment of the invention provides a substrate that the receiver circuit is grown on. The circuit has a first and second local oscillator. A mixer converts a received signal to a first IF frequency. A first buffer amplifier is cascaded after the mixer and then the first IF is routed to an external first differential filter assembly. The first differential filter assembly is coupled to the first buffer amplifier output for removing an image distortion and removing unwanted channels from the first IF. A second buffer amplifier having its circuit elements disposed upon the substrate is coupled to the external first differential filter assembly output.
Next, a first I/Q mixer disposed upon the substrate for converting the first IF to a second IF I and Q signal and rejecting a first IF image distortion is provided. A poly phase circuit for combining the second IF I and Q signals into a second IF signal is cascaded after the first I/Q mixer. A third buffer amplifier having its circuit elements disposed upon the substrate and cascaded after the poly phase circuit is next encountered.
An external second differential filter assembly coupled to the third buffer amplifier output, for removing an image distortion from the second IF and removing unwanted channels is finally provided.
Many of the attendant features of this invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description considered in connection with the accompanying drawings, in which like reference symbols designate like parts throughout.